Idle Air Control Valve?
Throttle position sensor?
One rare circumstatnce I ran into on a 91 GMC Sierra .... Three loose screws
on the top of the throttle body? Perhaps anpther vacuum leak somewhere else?

Well, thanks for your inputs!
Maybe I could be more accurate !
The idle is fine (or close to) when the car is not running, but erratic when
the car runs at low speed / low rpm. Moreover, the engine works fine as long
as I push the accelerator and idle only starts to be erratic when
decelerating under 1500 rpm.
If this can help you to help me!
Rgds
Phil

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